A type of endoprosthesis device, commonly referred to as a stent, may be placed or implanted within a vein, artery or other tubular body organ for treating occlusions, stenoses, or aneurysms of a vessel by reinforcing the wall of the vessel or by expanding the vessel. Stents have been used to treat dissections in blood vessel walls caused by balloon angioplasty of the coronary arteries as well as peripheral arteries and to improve angioplasty results by preventing elastic recoil and remodeling of the vessel wall. Two randomized multicenter trials have recently shown a lower restenosis rate in stent treated coronary arteries compared with balloon angioplasty alone (Serruys, PW et al. New England Journal of Medicine 331: 489-495, 1994, Fischman, DL et al. New England Journal of Medicine 331:496-501, 1994). Stents have been successfully implanted in the urinary tract, the bile duct, the esophagus and the tracheo-bronchial tree to reinforce those body organs, as well as implanted into the neurovascular, peripheral vascular, coronary, cardiac, and renal systems, among others. The term xe2x80x9cstentxe2x80x9d as used in this Application is a device which is intraluminally implanted within bodily vessels to reinforce collapsing, dissected, partially occluded, weakened, diseased or abnormally dilated or small segments of a vessel wall.
One of the drawbacks of conventional stents is that they are generally produced in a straight tubular configuration. The use of such stents to treat diseased vessels at or near a bifurcation (branch point) of a vessel may create a risk of compromising the degree of patency of the primary vessel and/or its branches, or the bifurcation point and also limits the ability to insert a second stent into the side branch if the result of treatment of the primary, or main, vessel is suboptimal. Suboptimal results may occur as a result of several mechanisms, such as displacing diseased tissue, plaque shifting, vessel spasm, dissection with or without intimal flaps, thrombosis, and embolism.
The risk of branch compromise is increased generally in two anatomical situations. First, a side branch may be compromised when there is a stenosis in the origin of the side branch. Second, when there is an eccentric lesion at the bifurcation site, asymmetric expansion can cause either plaque shifting or dissection at the side branch origin. There are reports of attempts to solve this problem by inserting a balloon into the side branch through the struts of a stent deployed in the main branch spanning the bifurcation point; however, this technique carries the risk of balloon entrapment and other major complications (Nakamura, S. et al., Catheterization and Cardiovascular Diagnosis 34: 353-361 (1995)). Moreover, adequate dilation of the side branch is limited by elastic recoil of the origin of the side branch. In addition, insertion of a traditional stent into a main vessel spanning a the bifurcation point may pose a limitation to blood flow and access to the side branch vessel. The term xe2x80x9cstent jailxe2x80x9d is often used to describe this concept. In this regard, the tubular slotted hinged design of the Palmaz-Schatz intracoronary stent, in particular, is felt to be unfavorable for lesions with a large side branch and is generally believed to pose a higher risk of side branch vessel entrapment where the stent prevents or limits access to the side branch. Id.
One common procedure for intraluminally implanting a stent is to first open the relevant region of the vessel with a balloon catheter and then place the stent in a position that bridges the treated portion of the vessel in order to prevent elastic recoil and restenosis of that segment. The angioplasty of the bifurcation lesion has traditionally been performed using the xe2x80x9ckissingxe2x80x9d balloon technique where two guidewires and two balloons are inserted, one into the main branch and the other into the side branch. Stent placement in this situation requires the removal of the guidewire from the side branch and reinsertion through the stent struts, followed by the insertion of a balloon through the struts of the stent along the guidewire. The first removal of the guidewire poses the risk of occlusion of the side branch during the deployment of the stent in the main branch.
In general, when treating a bifurcation lesion using commercially available stents, it is important to cover the origin of the branch because if left uncovered, this area is prone to restenosis. In order to cover the branch origin, conventional stents inserted into the branch must protrude into the lumen of the main artery or vessel from the branch (which may cause thrombosis, again compromising blood flow). Another frequent complication experienced when stenting bifurcated vessels is the narrowing or occlusion of the origin of a side branch spanned by a stent placed in the main branch. Additionally, placement of a stent into a main vessel where the stent partially or completely extends across the opening of a branch makes future access into such branch vessels difficult if not impossible. As a result, conventional stents are often placed into the branch close to the origin, but generally not covering the origin of the bifurcation.
Lastly, conventional stents are difficult to visualize during and after deployment, and in general are not readily imaged by using low-cost and easy methods such as x-ray or ultrasound imaging. While some prior art balloon catheters (and not stents) are xe2x80x9cmarkedxe2x80x9d at the proximal and distal ends of the balloon with imageable patches, few stents are currently available which are marked with or which are at least partly constructed of, a material which is imageable by currently known imaging procedures commonly used when inserting the stents into a vessel, such as ultrasound or x-ray imaging. The invention described in this Application would not work with endoscopy as currently used as an imaging method due to size limitations, but future advances in limiting the size of endoscopic imaging devices may in the future make endoscopic imaging compatible with the stents of the invention.
Accordingly, there is a need for improved stent apparatuses, most particularly for applications within the cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular systems and the brain which 1) completely covers the bifurcation point of bifurcation vessels; 2) may be used to treat lesions in one branch of a bifurcation while preserving access to the other branch for future treatment; 3) allows for differential sizing of the stents in a bifurcated stent apparatus even after the main stent is implanted; 4) may be delivered intraluminally by catheter; 5) may be used to treat bifurcation lesions in a bifurcated vessel where the branch vessel extends from the side of the main vessel; and 6) is marked with, or at least partly constructed of, material which is imageable by commonly used intraluminal catheterization visualization techniques including but not limited to ultrasound or x-ray.
The present invention concerns novel stent apparatuses for methods, and kits use in treating lesions at or near the bifurcation point in bifurcated vessels. More particularly, the invention concerns a stent apparatus with a main tubular stent body having at least one side opening which may further comprise an extendable or second stent inserted through the side opening and at least partly in registry with the wall of the side opening.
As used herein, the term xe2x80x9cvesselxe2x80x9d means any body lumen or tubular tissue within the cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular systems and the brain. Devices constructed in accordance with the invention include, singularly or in combination, a main expandable tubular stent body having at least one side opening (usually substantially circular) located between its proximal and distal end openings, which side opening may further comprise a radially expandable portion extending laterally outward from the edges of the side opening; and an expandable branch second stent comprising proximal and distal end openings and which may further comprise a contacting portion at its proximal end, and which may be constructed to form an angularly variable branched stent apparatus when inserted through a side opening of the main stent. The radially expandable portion preferably comprises a plurality of laterally deployable elements, such as loops, tabs, beams, or the like, attached or coupled to a peripheral edge of the side opening. Usually, the elements will project inwardly from the periphery into the side hole so that they may be deployed radially outwardly from the periphery to open in a petal-like fashion. The elements may be formed integrally as part of the tubular body structure, e.g., being formed from the bent wire or band or from the cut tubular structure which defines the stent structure. Alternatively, they could be formed separately and subsequently attached by crimping, welding, folding, interference fitting, etc. Optionally, the expandable portion may be covered with a fabric or the entire stent structure membrane to help form the transition between the main body lumen and the lumen of the second stent. The stents of the invention are marked with, or at least partially constructed of, a material which is imageable during intraluminal catheterization techniques, most preferably but not limited to ultrasound and x-ray, preferably being radiopaque.
In a preferred aspect of the stent design, the side hole will be defined by a continuous band or pattern of material which defines the periphery of the side hole. The band may have a circular, oval, or other regular geometry in which case the width and area of the side hole will remain generally constant as the stent is expanded. Alternatively, the continuous band may comprise discontinuities over its length so that the area and/or width of the side hole may expand together with the stent structure. Preferably, the continuous band will include inwardly projecting loops, fingers, or other protrusions which will define the laterally deployable elements which project inwardly from the peripheral edge of the side opening. The inwardly projecting loops or other elements may be overlapping or non-overlapping. The use of overlapping looped structures maximizes the length of the inwardly projecting elements after they are unfolded and opened inwardly into the side branch, as described in more detail below.
In another aspect of the present invention, a stent for placement in a bifurcated body lumen comprises a main tubular body having a first end, a second end, and a side opening therebetween. A first portion of the main tubular body between the first end and the side hole opens in response to a first radially outward pressure, typically provided by an expansion balloon. A second portion of the main tubular body between the side hole and the second end opens in response to a second pressure, again typically applied by an expansion balloon. By constructing the main tubular body so that the first opening pressure is less than the second opening pressure, the stent can have differential opening characteristics. That is, by introducing a balloon expansion catheter into the stent and applying a constant pressure over the entire length of the balloon, the first portion of the stent will yield and open before the second portion of the stent. The particular embodiments described below, the first yield pressure will typically be in the range from 1 atmospheres to 10 atmospheres while the second yield pressure will typically be in the range from 2 atmospheres to 18 atmospheres. Such stent structures may be placed by initially opening and deploying the first portion, typically the proximal portion on the same side of the bifurcation as the deployment catheter, and thereafter positioning the side hole to align more precisely with the bifurcated secondary blood vessel. After the proper positioning has been achieved, the second stent portion can then be opened, conveniently using the same expansion balloon which has been inflated to a higher inflation pressure. Such stents will typically include the laterally deployable elements disposed around the side opening, as described above, and will optionally be used in combination with secondary stents, as described above.
The stent structures as described previously may combine conventional stent elements, such as serpentine rings, diamond or box structures, axial expansion members, and the like. In addition, in order to provide the differential expansion characteristics, the main tubular bodies of the stents may include axial spine structures which differ from the remaining portions of the tubular body of the stent. For example, the first portion of the stent may have an axial spine which readily expands circumferentially. By then providing a spine section on the second portion of the stent which is more resistant to circumferential expansion, the desired differential expansion will be achieved. Alternatively, the differential expansion can be achieved by employing stent patterns which are uniformly easier or more difficult to radially expand over their entire peripheral length. Specific examples of both structures will be described below.
The stent apparatuses of the invention offers significant and novel advantages over prior art stents in that the stents of the invention 1) can completely cover the bifurcation point of a branched vessel; 2) can accommodate main and branch stents of differing sizes, thus providing a better fit where the main and branch vessels are of different sizes or where the main and branch vessels are occluded to different degrees; 3) can fit branched vessels where the branch extends laterally from the side of the main vessel; 4) may be used to treat lesions in one branch of a bifurcation while preserving complete access to the other branch for future treatment; 5) may be delivered intraluminally by catheter; and 6) are marked with, or at least partly constructed of, material which is imageable by commonly used intraluminal catheterization visualization techniques including but not limited to ultrasound or x-ray, but not endoscopy.
Thus, it is an object of the present invention to provide both a double-stent apparatus and a single-stent apparatus, each of which may be used to cover the origin of a bifurcation in a branched vessel.
Another object of the invention is to provide a single-stent apparatus which may be used to treat only one branch of a bifurcation lesion while leaving access to the second branch unobstructed.
Additionally, it is an object of the invention to provide a stent apparatus which is itself imageable by methods commonly used during catheterization such as x-ray or ultrasound.
Yet another object of the invention is to provide a bifurcating double-stent device wherein the main stent and the branch stent or stents may be of different sizes.
Lastly, it is an important object of the invention to provide a stent apparatus which may be used to treat bifurcated vessels where the vessel bifurcation extends laterally from the side of the main vessel.
These objects and other object advantages and features of the invention will become better understood from the detailed description of the invention and the accompanying drawings.